(AlxGa1-x)1-yInyP LEDs are used to produce visible wavelengths from red to amber. AlInGaP LEDs are typically formed by growing epitaxial layers, including p-type and n-type layers sandwiching a light-emitting active layer, on a GaAs growth substrate. High quality ternary and quaternary substrates are very difficult to fabricate, so GaAs substrates are commonly used. To produce low-defect LED layers, the lattice constant of the (AlxGa1-x)1-yInyP epitaxial layers must match the lattice constant of the GaAs. To match the GaAs lattice constant, y=0.48. The x value is adjusted to achieve the desired emission wavelength.
The light output of AlInGaP LEDs is highly dependent on temperature. For example, at temperatures in the range of 80-120 degrees C., the internal quantum efficiency at useful wavelengths is significantly reduced, resulting in a light output of two-thirds to one-half of the light output at room temperature. This variation in light output is extremely significant in certain applications such as traffic lights, tail lights, and displays.
What is needed is a technique to reduce the temperature sensitivity of AlInGaP LEDs.